Since it is the most important and not who is your favorite I said Melvins, Soundgarden, Other (Green River), and Mudhoney.
With out the first three the sound would not be there. With out Mudhoney and their single Touch Me I'm Sick, which got them them touring with Sonic Youth and in the British press, Nirvana, Ailice in Chains, and Pearl Jam would not have exploded the way they did because no one would have thought to look in Seattle if not for their single and the press it created.